1. Field of the Invention
The present invention relates to a system for storing data consisting of a plurality of data storing units, a controller for controlling the reading and writing of data and al redundant data storing unit for storing redundant data, and the method of controlling the writing of redundant data.
2. Description of the Related Art
To prevent video data and audio data which are provided to users in the field of multimedia from being interrupted, it is necessary that the consecutive accesses to data to be read and written should be guaranteed. A technology for accessing video data without interruption is widely used by a system such as video-on-demand for providing video images, etc. To provide these services it is necessary to take measures to cope with failures which might occur in such a system.
When constructing a system such as video-on-demand, etc., to provide many users with high-quality images, it is necessary to access data making the best use of the transfer efficiency of a bus for transferring the data, and to provide a parity disk for recovering without delay from a failure which might occur in the system.
As a technology for coping with the problems of high-speed access and reliability, the redundant array of inexpensive disks (RAID) is publicly known. In RAID, since parity calculation and the writing on a parity disk of parity data are automatically carried out, the timing in the use of a bus for writing the parity data cannot be controlled from the controller side for controlling the reading from and writing to a data storing unit of the data. For example, the writing on the parity disk of parity data has been carried out at the timing for accessing the data storing unit, and thereby the reading from the data storing unit of data or the writing to the data storing unit of data, has been disturbed. For this reason, the efficiency of the use of a bus must be reduced to cope with even the case where access to a parity disk occurs at an unexpected timing.
On the other hand, in the operation of a multimedia service such as video-on-demand, etc., since the access schedule of the data storing unit is complicated, and it is necessary to completely guarantee the predetermined schedule, it becomes a problem that a process such as the writing on the parity disk of parity data, etc. occurs at an unexpected timing.
It is an object of the present invention to implement the writing in a redundant data storing unit of redundant data without disturbing access to a data recording unit. It is another object of this invention to improve the efficiency of the use of a bus.
The data storing system of the present invention, consisting of a plurality of data storing units for storing data, a redundant data storing unit for storing the redundant data of the data written in the data storing unit and a controller for controlling the reading from and writing to the data storing unit of data, comprises a redundant data controller further comprising a calculating unit for calculating the redundant data of data written in the data storing unit and a redundant data storing unit for storing redundant data obtained by the calculating unit, and the controller controls the reading from and writing to the data storing unit of data and the writing in the redundant data storing unit of the redundant data obtained by the redundant data controller.
Since by adopting the present invention both the calculation of redundant data and the storing of the result of the calculation are carried out by a redundant data controller, and the control of both the writing in a redundant data storing unit of redundant data and the reading from and writing to a data storing unit of data are carried out by a controller, both accesses to the data storing unit and to the redundant data storing unit can be comprehensively controlled by the controller. Therefore, access to the data storing unit is prevented from being disturbed by the writing to the redundant data storing unit of redundant data. Furthermore, since both the accesses to the data storing unit and to the redundant data storing unit can be controlled by the controller, a high-density access schedule can be planned and maintained, by which ;the reliability of a system can be enhanced and the efficient of the use of a bus can be improved.